Preheat oven to 350 F. Line 12 Muffin Cups with foil liners. "I use my pan with the squares". (spray with cooking spray, no matter what you use.)
Melt semi-sweet chips & butter together in a large microwave bowl and microwave at 50% for 1 minute, stir and microwave for a further minute. Stir again and repeat until mixture is smooth. Let Cool slightly.
Whisk eggs, sugar, vanilla & salt into the melted chocolate.
Fold in flour, just until incorporated. Add milk chocolate chips and nuts. Fill prepared muffin cups & top each with additional milk chocolate chips.
Bake for 35 - 40 minutes or less (depending on size of your muffins), let set about 5 min., and then remove from the pan and cool on rack.